A conventional motor using a dynamic pressure gas bearing that supports a shaft by a sleeve is described in Japanese Laid-Open Patent 2014-073068 and shown particularly in FIG. 1 of that patent.
However, the above conventional motor has a structure in which the rotation of the shaft simply generates a dynamic pressure between an outer circumferential surface of the shaft and an inner circumferential surface of the sleeve to create a bearing rigidity.
Thus, when an external disturbance acts on the motor, for example, to cause the shaft and the sleeve to swing in a relative manner in a direction along which the rotation axis of the rotating body inclines and contact with each other, the contact friction of the dynamic pressure gas bearing increases, which could cause seizing of the dynamic pressure gas bearing such as adhesion and burning.
In order to maintain the rotation safely, another motor is known that has a sliding bearing, a rolling bearing provided at an outer side of the sliding bearing, and rotation regulating means for regulating the rotation of the rolling bearing until a rotation torque transmitted from the sliding bearing to the rolling bearing reaches or exceeds a standard rotation torque. An example of a motor designed to maintain safe rotation is the motor described in Japanese Laid-Open Utility Model No. S57-1132, particularly in FIGS. 1 to 3 and 6.
However, the above conventional rotation regulating means has a contact structure in which an elastic member and a connection member, which are attached to an outer annular member, abut on an inner annular member. Thus, there is a problem that the elastic member still abuts on the inner annular member at each rotation of the rolling bearing and may get broken even after the transmitted rotation torque exceeds the standard rotation torque and the rotation of the rolling bearing starts, or a problem that the connection member fractures when the transmitted rotation torque exceeds the standard rotation torque, causing the structure itself of the rotation regulating means to be broken.